302
FXUS02 KWBC 111916
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
316 PM EDT MON MAR 11 2024
VALID 12Z THU MAR 14 2024 - 12Z MON MAR 18 2024
...HEAVY SNOWS POSSIBLE ACROSS PARTS OF THE CENTRAL-SOUTHERN
ROCKIES ON THURSDAY INTO FRIDAY...
..HEAVY RAINFALL POTENTIAL RETURNS TO THE SOUTH LATE THIS WEEK
..OVERVIEW
THE GENERAL FLOW OVER THE CONUS WILL BE SETTLING INTO A MUCH MORE
AMPLIFIED REGIME DURING THE MEDIUM RANGE PERIOD. ALREADY AT THE
START OF THE FORECAST ON THURSDAY, A SHARP/AMPLIFIED UPPER RIDGE
OFF THE WEST COAST WILL SUPPORT A WESTERN TROUGH AND EMBEDDED DEEP
SOUTHWEST UPPER LOW THAT WILL LIKELY MEANDER IN PLACE FOR MUCH OF
THE PERIOD. THIS FEATURE WOULD PROMOTE A POSSIBLY SIGNIFICANT
WINTER STORM ACROSS THE COLORADO ROCKIES ON THURSDAY WITH SOME
SNOW PERSISTING OVER THE SOUTHERN ROCKIES INTO FRIDAY, ALONG WITH
A MULTI-DAY PERIOD OF HEAVY RAINFALL POTENTIAL ACROSS PARTS OF THE
SOUTHERN U.S. LATE THIS WEEK AND INTO THE WEEKEND. A LEADING PLAINS
THROUGH NORTHEAST SYSTEM MAY ALSO PRODUCE SOME ENHANCED RAINFALL
NEAR ITS TRACK LATE THIS WEEK. THE EAST PACIFIC INTO WESTERN CANADA
UPPER RIDGE WILL HELP TO AMPLIFY DOWNSTREAM TROUGHING INTO THE
EASTERN HALF TO TWO-THIRDS OF THE LOWER 48 BY THIS COMING WEEKEND
INTO EARLY NEXT WEEK, WITH A COLDER TREND BEHIND A NORTHERN TIER TO
EAST COAST FRONT.
..GUIDANCE/PREDICTABILITY ASSESSMENT
WITHIN THE FAIRLY AGREEABLE LARGE SCALE FORECAST, THE TWO GREATEST
UNCERTAINTIES INVOLVE THE WAVE TRACKING FROM THE CENTRAL
PLAINS/MIDWEST THROUGH THE NORTHEAST LATE THIS WEEK AND WHETHER
THE UPPER LOW OVER THE SOUTHWEST ULTIMATELY BEGINS TO PHASE WITH
THE AMPLIFYING UPPER TROUGH TO THE EAST OF THE ROCKIES BY LATE
WEEKEND/EARLY NEXT WEEK.
FOR THE WAVE LATE THIS WEEK, THE CONSENSUS OF 00Z/06Z GUIDANCE
INCLUDING THE ECMWF-INITIALIZED MACHINE LEARNING (ML) MODELS
SUGGESTED THAT THE GFS FROM THOSE CYCLES WAS TOO FAST WHILE THE
00Z ECMWF COULD BE A TAD SLOW (MAINLY ON THURSDAY). THE 00Z
UKMET/CMC WERE CLOSEST TO THE MAJORITY SCENARIO. THE MAIN PRIORITY
FOR THIS PART OF THE FORECAST WAS TO DOWNPLAY 00Z/06Z GFS
INFLUENCE. A SLOWER TREND IN THE 12Z GFS HAS IMPROVED MODEL
AGREEMENT IN THE NEW CYCLE. LATEST CLUSTERING SUGGESTS THIS COULD
BECOME A FAIRLY VIGOROUS (BUT PROGRESSIVE) WAVE OFF THE NEW ENGLAND
COAST BY EARLY FRIDAY. THE 00Z ML MODELS STILL SHOWED QUITE A BIT
OF SPREAD FOR STRENGTH AND LATITUDE OF THE SURFACE WAVE AT THAT
TIME THOUGH. THIS OVERALL FEATURE SEEMS TO HAVE BELOW AVERAGE
PREDICTABILITY, GIVEN A COMBINATION OF UPPER DYNAMIC SUPPORT
STREAMING FROM THE SOUTHWEST UPPER LOW AND APPROACHING NORTHERN
STREAM ENERGY.
FOR THE SOUTHWEST UPPER LOW, THE 00Z ML MODELS ARE REMARKABLY
SIMILAR IN KEEPING THE FEATURE SEPARATE FROM TROUGHING TO THE
NORTHEAST INTO NEXT MONDAY, IN A SOMEWHAT BETTER DEFINED FASHION
THAN THE GEFS/ECENS/CMCENS MEANS THAT ALSO KEEP THE TWO SEPARATE.
DYNAMICAL MODELS ARE SPLIT, WITH LATEST CMC RUNS AND 00Z GFS
SEPARATE BUT 06Z/12Z GFS AND LATEST ECMWF RUNS TRENDING TOWARD
MORE PHASING (ALBEIT WITH THE 12Z ECMWF DELAYING THIS JUST A TAD).
CURRENT PREFERENCE LEANED TOWARD THE MORE SEPARATE SOLUTION
FAVORED BY THE MEANS AND CORRESPONDING OPERATIONAL MODEL RUNS.
THE UPDATED FORECAST STARTED WITH A COMPOSITE OF THE 00Z/06Z
OPERATIONAL MODELS DURING THE FIRST HALF OF THE PERIOD, WITH
SOMEWHAT LESS THAN TYPICAL GFS WEIGHT DUE TO AFOREMENTIONED
CONSIDERATIONS FOR THE NORTHERN STREAM WAVE. THEN THE ENSEMBLE
MEAN AND 00Z GFS/CMC PREFERENCE FOR THE OVERALL PATTERN FAVORED A
RAPID TRANSITION TO EMPHASIZING THE MEANS AND THOSE MODEL RUNS LATE
IN THE PERIOD. THIS SOLUTION KEPT GFS WEIGHT LOW ENOUGH NOT TO
PLACE TOO MUCH WEIGHT ON THAT MODEL'S POSSIBLE OVER-DAMPENING OF
THE WESTERN CANADA UPPER RIDGE NEXT MONDAY.
..WEATHER/HAZARDS HIGHLIGHTS
A LONG-DURATION WINTER STORM WILL BE ONGOING ACROSS PARTS OF THE
CENTRAL-SOUTHERN ROCKIES AS THE PERIOD BEGINS THURSDAY, WITH
POSSIBLY SIGNIFICANT SNOWFALL IN THE HIGHEST TERRAIN OF COLORADO,
AND MORE UNCERTAIN POTENTIAL FOR NOTABLE SNOWS ACROSS THE FRONT
RANGE URBAN CORRIDOR AS WELL. SNOWS SHOULD SHIFT SOUTHWARD INTO
NEW MEXICO BY FRIDAY WHILE POSSIBLY LINGERING OVER SOUTHERN
COLORADO AS WELL. FARTHER EAST, A CENTRAL PLAINS/MIDWEST THROUGH
NORTHEAST WAVE AND FRONTAL SYSTEM WILL SUPPORT SOME ENHANCED
PRECIPITATION NEAR ITS PATH DURING THURSDAY-FRIDAY. ON DAY
4/THURSDAY, LATEST TRENDS TOWARD THE MIDDLE/SLOWER PART OF THE
ENVELOPE FOR THIS WAVE PLUS FAVORABLE MOISTURE/INSTABILITY IN THE
WARM SECTOR, A SUBSET OF OPERATIONAL MODELS WITH LOCALLY
SIGNIFICANT QPF, AND SHORTER-TERM RAINFALL POSSIBLY TEMPERING DRY
ANTECEDENT CONDITIONS, SEEM TO FAVOR EXPANDING THE MARGINAL RISK
AREA AS FAR NORTH AS ILLINOIS AND VICINITY. THEN BY DAY 5/FRIDAY
THERE IS INCREASED CLUSTERING TOWARD AN AXIS OF POTENTIALLY
SIGNIFICANT RAINFALL EXTENDING INTO THE NORTHEAST (POSSIBLY WITH
SOME INSTABILITY), WITH THE NORTHERN PART OF THE OVERALL MARGINAL
RISK AREA INCORPORATING THIS MAJORITY SCENARIO. SOME MOISTURE
REACHING FAR NORTHERN NEW ENGLAND COULD PRODUCE A LITTLE SNOW.
MEANWHILE THE MOISTURE STREAMING NORTHWARD AHEAD OF THE
STAGNANT UPPER LOW OVER THE SOUTHWEST AND INTERACTING WITH THE
FRONT TRAILING FROM THE AFOREMENTIONED NORTHERN WAVE WILL SUPPORT
WHAT SHOULD BE A MULTI- DAY HEAVY RAINFALL THREAT ACROSS THE SOUTH.
THERE REMAINS PLENTY OF UNCERTAINTY IN THE EXACT PLACEMENT OF THE
HIGHEST QPF, BUT THERE IS SUPPORT IN THE DYNAMICS FOR FAIRLY BROAD
SLIGHT RISK AREAS ON THE DAYS 4 AND 5 EXCESSIVE RAINFALL OUTLOOKS.
FOR DAY 4, THE SLIGHT RISK EXTENDS FROM NORTHEAST TEXAS/SOUTHEAST
OKLAHOMA THROUGH MUCH OF ARKANSAS AND INTO NEARBY PARTS OF
LOUISIANA/MISSISSIPPI. THE SLIGHT RISK AREA SHIFTS TO THE SOUTH AND
EAST ON DAY 5 MORE INTO FAR EASTERN TEXAS THROUGH LOUISIANA AND
THE CENTRAL GULF COAST STATES. SEVERE WEATHER IS ALSO A THREAT WITH
THIS CONVECTIVE ACTIVITY PER THE STORM PREDICTION CENTER WITH A
SEVERE WEATHER AREA DELINEATED FOR PARTS OF THE SOUTHERN PLAINS ON
THURSDAY. SOME HEAVY RAINFALL POTENTIAL MAY EXTEND NORTHWARD ALONG
THE BOUNDARY INTO THE SOUTHERN/CENTRAL APPALACHIANS. HEAVY RAINFALL
MAY CONTINUE INTO PARTS OF THE SOUTHEAST THIS WEEKEND AS WELL. THE
SYSTEM TRACKING THROUGH SOUTHEASTERN CANADA SATURDAY-MONDAY AND
TRAILING FRONT MAY PRODUCE AREAS OF RAIN AND PERHAPS COLD SECTOR
SNOW OVER PARTS OF THE GREAT LAKES/NORTHEAST.
MEAN RIDGING ALOFT OVER THE EASTERN U.S. WILL SUPPORT AN EXPANSIVE
AREA OF ABOVE NORMAL TEMPERATURES TO THE EAST OF THE ROCKIES. THE
CORE OF WARMEST ANOMALIES SHOULD EXTEND FROM THE MIDWEST INTO THE
NORTHEAST LATE THIS WEEK, WITH HIGHS POTENTIALLY REACHING 15-20+
DEGREES ABOVE NORMAL. TEMPERATURES ACROSS THE EAST WILL TREND
COOLER WITH TIME AFTER THURSDAY, BUT SHOULD GENERALLY REMAIN ABOVE
NORMAL THROUGH THE WEEKEND. OVER THE WEST, MODERATELY BELOW
AVERAGE HIGHS AND NEAR/ABOVE AVERAGE LOWS WILL SHIFT INTO THE
GREAT BASIN/FOUR CORNERS THURSDAY AND BEYOND. BELOW AVERAGE
TEMPERATURES WILL ALSO SPREAD FROM THE NORTH-CENTRAL U.S. INTO THE
MISSISSIPPI VALLEY AND EVENTUALLY THE MIDWEST THIS WEEKEND/EARLY
NEXT WEEK AS NORTHERN STREAM TROUGHING MOVES THROUGH THE REGION.
TEMPERATURES ALONG THE IMMEDIATE WEST COAST SHOULD INCREASE BY
FRIDAY AND THROUGH THE WEEKEND AS STRONG RIDGING BUILDS IN ALOFT,
WITH THE NORTHWEST SEEING THE BEST POTENTIAL FOR SOME HIGHS
REACHING 10-15 DEGREES ABOVE NORMAL.
RAUSCH/SANTORELLI
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES ARE AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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